The present invention relates to power supplies for electronic devices, such as video cameras. More particularly, the present invention relates to the combination of a primary battery pack and detachable reserve battery pack for use with video cameras.
Portable battery products for professional video cameras are designed with three predominant features in mind. These features include: 1) how much does a battery weigh; 2) how long will the camera run with the particular battery; and 3) is the battery reliable under a variety of loads and conditions.
The weight of a camera battery is of extreme importance to professional cameramen as the camera alone weighs between 10 lbs. and 15 lbs. In addition, earlier prior art batteries typically weighed 5 lbs. or more which had a noticeable effect on the overall weight carried by the cameramen. Nonetheless, the early 5 lb. batteries were reliable and provided at least 60 w hours of capacity. Since the power consumption of professional cameras is typically between 20 w and 30 w without activation of a camera light, and between 45 w and 50 w with activation of a camera light, the 5 lb. batteries provided at least an hour of camera operation.
Eventually, advanced lightweight battery chemistries were developed for video camera applications. Unfortunately, most of the chemistries provided high capacity under minimum load conditions which are far below professional video standards. For example, recent lithium ion batteries are susceptible to routine current surges which occur such as when the camera light is activated. For example, a 25 w camera lamp can initially draw up to 100 w for a few milliseconds.
Lithium ion batteries often cannot handle this current surge resulting in the lithium ion battery surge protector disabling the battery, and thereby freezing the camera. To reactivate the battery, the battery is typically removed and then reinstalled. Thus, while recent battery chemistries can provide improved watt hour capacity, the battery chemistries often times can not produce the surge current capabilities required. Unfortunately, this has resulted in batteries being branded as unreliable. With reference to FIG. 1, professional cameramen have attempted to overcome this disadvantage by wiring two batteries in parallel, thereby spreading the load over two batteries rather than one. To this end, a first battery is mounted to the camera in typical manner. A second battery, often located on the cameraman""s belt, is then connected in parallel to the first battery by wires.
Unfortunately, though producing longer camera run times, this solution presents several additional disadvantages. First, the positioning and wiring of a second battery can be difficult and annoying. Furthermore, providing two batteries in parallel has produced unreliable behavior as the batteries should be of equal capacity. In addition, the batteries need to be electrically isolated from charging each other. Moreover, reliability becomes of greater concern when simultaneously using two batteries, rather than one.
Various additional attempts have been developed for providing more reliable and expandable power supplies. For example, the combination of a primary battery and auxiliary battery has been used for some time in connection with laptop computers. As described in U.S. Pat. No. 5,347,163, such systems typically include a voltage detection circuit which detects the voltage of the primary battery, and the system switches power from the primary battery to the auxiliary battery when the detected voltage falls below a predetermined threshold. Unfortunately, such systems will not protect against current surges, such as caused by the activation of a camera light. Moreover, the combination of a primary battery and auxiliary battery are typically used in cooperation with electrical devices, such as laptop computers, which include constructions specifically designed to accept two batteries. Conventional video cameras are not constructed to accept two batteries.
Meanwhile, U.S. Pat. No. 4,816,862 describes a power supply system for a camera. The power supply system includes a main battery and a back-up battery. When the main battery is removed, the back-up battery supplies power to the camera""s micro computer so that the computer""s processor and internal memory is maintained in a properly operating condition after the main battery has been removed. However, once the main battery has been removed or discharged, the camera""s flash circuit and motor circuit are disabled so that the camera is inoperable.
Similarly, U.S. Pat. No. 5,164,761 describes a battery system for a handheld camera. The battery system includes a primary non-rechargeable battery, and a rechargeable secondary battery. When the primary battery is discharged, a switch is activated to switch power from the primary battery to the secondary battery. Again, the system does not provide for protection against current surges.
In addition, U.S. Pat. No. 6,289,179 discloses a power system for handheld cameras. The power system includes a structure for stacking any number of batteries and for connecting such batteries in parallel. However, the power system does not provide a reserve power supply so that the camera can still be utilized when the batteries are replaced after discharge.
There is thus a significant need for an improved power supply for electrical devices, such as video cameras.
In addition, it would be advantageous that the power supply provide power to an electrical device when the primary battery was being replaced.
In addition, it would highly advantageous if the power supply included a primary battery pack which charges a reserve battery pack so that the reserve battery pack need not be removed for charging.
Furthermore, it would be highly advantageous if the improved power supply could be used in cooperation with electrical devices which are not initially designed to accept two battery packs, but instead utilize only a single primary battery pack.
Briefly, in accordance with the invention, I provide an improved power supply for electrically powered devices, which is particularly suitable for professional video cameras. The power supply includes a main battery pack and reserve battery pack. Moreover, the combination of a main battery pack and reserve battery pack are constructed to connect to a device initially constructed to use only a single primary battery pack. To this end, the reserve battery pack includes first and second mounting surfaces, and first and second sets of power terminals. The main battery pack includes a pair of electrical power terminals, and the main battery pack attaches to the reserve battery pack by means of a first mount. The first mount is constructed to detachably affix the main battery pack to the reserve battery pack with the main battery pack""s electrical power terminals engaging and electrically coupling to the reserve pack""s first set of power terminals.
Meanwhile, the reserve battery pack""s second mount is constructed to attach and engage to the electrical powered device""s mounting structure with the reserve pack""s second set power terminals engaging the electrical powered device""s electrical terminals so that charge within the reserve pack can be provided to the electrically powered device. The mounting structures for coupling the main battery pack to the reserve battery pack, and for coupling the reserve battery pack to the electrically powered device, may take various forms as can be determined by those skilled in the art. However, in a preferred embodiment, the first and second mount constructions permit the main battery pack to affix to the reserve battery pack with the main battery pack""s terminals engaging the reserve pack""s first terminals, and alternatively permit the main battery pack to connect directly to the electrically powered device""s power terminals so that the electrically powered device may be operated with, or without, using the reserve battery pack.
The power supply of the present invention further includes a controller for controlling the electrical connection of the main battery pack and reserve battery pack to the electrically powered device. To this end, the controller includes a detector for detecting the voltage of the main battery pack and reserve battery pack, and for detecting current draw from the electrically powered device. In addition, the controller includes a processor and a plurality of switches for controlling the electrical connection of the main battery pack and the reserve battery pack with the electrically powered device.
In operation, the controller selectively connects only the main battery pack to the electrically powered device, or electrically connects only the reserve battery pack to the electrically powered device, or electrically connects the main battery pack and reserve battery pack in parallel to provide power to the electrically powered device. The respective electrical connection is determined based upon predetermined charge and current parameters. For example, where the main battery pack and reserve battery pack are fully charged, the controller preferably actuates the switches so that the main battery pack alone provides power to the electrically powered device. However, if the electrically powered device initiates a current surge, detected by the detector, the control processor causes the main battery pack and reserve battery pack to be connected in parallel. Thereafter, the main battery pack and reserve battery pack are caused to remain connected in parallel until a predetermined time period has passed, such as one second, or until the current surge has dissipated below a predetermined level.
Moreover, the control processor also selectively switches power from the main battery pack to the reserve battery pack when the main battery pack charge has dissipated below a predetermined level. The determination of the main battery pack""s charge may be determined by numerous means known to those skilled in the art including using voltage and/or current measurements of the main battery. For example, a 12 v battery may exhibit a 15 v measurement when full, but an 11 v measurement when close to empty. Thus, in practicing the present invention, the control processor may selectively switch power from a 12 v main battery pack to the reserve battery pack when the voltage of the main battery pack drops below 11 v.
The controller may be located within the main battery pack housing, within the reserve battery pack housing, or even within the electrically powered device. Preferably, the controller is connected to a battery gauge for displaying the remaining charge of either the main battery pack or reserve battery pack. Furthermore, preferably the controller is connected to a manual switch to allow a person to manually switch from power being supplied from the main battery pack to power being supplied from the reserve battery pack. This manual switch is useful in case the operator wishes to disengage the main battery pack from the reserve battery pack, prior to the main battery pack reaching an empty condition. Thus, the main battery pack can be removed, and replaced or recharged, while the reserve pack provides uninterrupted power to the electrically powered device.
In a preferred embodiment of the invention, the main battery pack also provides for recharging of the reserve battery pack. For this embodiment of the invention, the main processor""s detector detects the charge level of the reserve pack. Upon determination by the controller that the reserve pack has a diminished charge and determination that the main battery pack has sufficient charge for recharging the reserve pack, the controller electrically couples the main battery pack to the reserve battery pack so as to recharge the reserve battery pack.
It is thus an object of the present invention to provide a power supply for electrically powered devices, and particularly for professional video cameras, which is not susceptible to problems caused by current surges.
It is also an object of the present invention to provide a power supply including both a primary battery pack and a disengageable reserve battery pack which can be connected to an electrically powered device initially constructed to connect only to a single primary battery pack.
Moreover, it is an object of the present invention to provide a power supply which provides uninterrupted power to an electrically powered device even after the main battery pack or reserve battery pack have been removed for replacement or recharging.
Furthermore, it is an object of the present invention to provide a power supply wherein the reserve battery pack can be recharged while still connected to the electrically powered device by the main battery pack.